The invention relates to the field of detectors for laser radiation and in particular, to detectors of high intensity laser radiation.
Studies have been performed to determine the physical nature of the process whereby laser radiation impinges upon a surface and couples energy into the surface in such a manner as to cause ionization of thin layers of the surface. Reports of these studies are found in the following prior art references: (1) "Coupling of CO.sub.2 Laser Energy into Ionized Blowoff Material", by J. F. Ready, Optics Letters, Vol. 2, No. 5, May 1978, pp. 130-132; (2) "Charge Separation and Target Voltages in Laser-Produced Plasmas", by J. S. Pearlman and G. H. Dahlbacka, Applied Physics Letters, Vol. 31, No. 7, October 1977, pp. 414-417; (3) "Direct Conversion of CO.sub.2 Laser Energy to High-Voltage Electrical Energy", by W. T. Silfvast and L. H. Szeto, abstract of a talk given at the CLEA Conference, June 1, 1978, IEEE Journal of Quantum Electronics, QE-13, September 1977, on p. 96D; (4) "Direct Conversion of CO.sub.2 Laser Energy to High Voltage Electrical Energy Using a Laser-Produced Plasma", by W. T. Silfvast and L. H. Szeto, Applied Physics Letters, Vol. 31, No. 11, December 1977, pp. 726-728; (5) "Use of Laser Radiation to Create a Strong Electron Source", by O. V. Bogdankevich, V. Yu Sudzilovskii and A. A. Lozhnikov, Soviet Physics-Technical Physics, Vol. 10, No. 11, May, 1966, pp. 1573-1574; and (6) "Laser-Induced Current Pulses From a Target In a Gas", by T. U. Arifov, G. A. Askar'yan, I. M. Raevskii and N. M. Tarasova, Soviet Physics JETP, Vol. 28, No. 2, February, 1969, pp. 201-202.
The surface ionization caused by laser radiation impinging upon the surface of a target material which is situated within an evacuated chamber is detected in these above-cited references by the presence of a voltage difference between the target material and the distant chamber wall. These studies of the basic physical phenomenon have not succeeded in producing a laser radiation detector because the output voltages fluctuated from pulse-to-pulse and were not reproductible in a reliable manner. Furthermore, the voltage detected was not linearly related to the intensity when the surface was exposed to laser radiation having intensities in the region of 10.sup.9 W/cm.sup.2.